Recently, in order to finish a large amount of prints in a short delivery time, light-sensitive materials for color photographic papers to be improved in terms of rapid processing have been demanded. As one of the methods for attaining this, a method to use silver chloride emulsions or silver bromochloride emulsion having a high silver chloride content for enhancing processing speed has been known. However, it has been known that silver chloride emulsions or silver bromochloride emulsions having a high silver chloride content have a low sensitivity.
As a method for enhancing sensitivity, it is known that a super sensitization method is useful. Super sensitization is described in Photographic Science and Engineering, Volume 13, pp. 13-17 (1969) and Volume 18, pp. 418-430 (1974) and The Theory of the Photographic Process 4th edition, page 259, published by MacMillan Inc., 1977. It is known that, by selecting suitable sensitizing dyes and super sensitizers, high sensitivity can be obtained.
Heretofore, many compounds such as stylbene, azaindene, mercaptoheterocycles, thiourea and condensed compounds between phenol and hexamethylenetetraamine have been known as a super sensitizer. For example, they are disclosed in U.S. Pat. Nos. 2,875,058, 3,340,064, 3,457,078, 3,458,318, 3,615,632, 3,695,888 and 4,011,083 and Japanese Patent Publication Open to Public Inspection (hereinafter referred to as "Japanese Patent OPI Publication") No. 203447/1986. However, it was discovered that, when a silver halide emulsion is subjected to super sensitization by the use of the above-mentioned conventional technology, increase in sensitivity is still insufficient, and that fluctuation in photographic sensitivity is noticeable after storage of raw products.
Storage stability of photographic light-sensitive materials is extremely critical for preventing deterioration in quality of the print finish. Therefore, the above-mentioned technologies are not practically desirable.
In Japanese Patent O.P.I. Publication No. 100048/1990, technology to incorporate crown ethers and cyclodextrine into silver halide light-sensitive materials as a coagulation-destroying compound for magenta dyes is disclosed. However, the object of this technology is to improve stability of magenta dye, and no suggestion is given with regard to super sensitization effects of the above-mentioned compounds.
Japanese Patent O.P.I. Publication No. 25833 discloses that tetrazole derivatives having a cyclic structure which serves as a chelating agent in a molecule provide super sensitization to silver bromide emulsions. However, there is no description in it about super sensitization effects to silver chloride or silver-chloride-rich silver bromochloride. In addition, there is no description about super sensitization effects on silver halide emulsions containing metal ions.
In Japanese Patent O.P.I. Publication Nos. 13923/1976 and 171947/1984, technology to enhance sensitivity by incorporating products of metal from VIII group into silver halide grains is disclosed. In addition, in U.S. Pat. No. 4,269,927, technology to enhance sensitivity by incorporating cadmium, zinc, copper and lead into silver halide grains having a silver chloride content ratio of 80 mol % or more is disclosed. In Japanese Patent O.P.I. Publication Nos. 20853/1990 and 20854/1990, technology to enhance sensitivity by incorporating a 6th-seat ligand complex having cyano ligand of rhenium, ruthenium osmium or iridium. However, in the above-mentioned methods, increase in sensitivity is insufficient so that additional enhancement of sensitivity has been demanded.